Qt中事件分发源代码剖析
Qt中事件传递顺序:
在一个应该程序中,会进入一个事件循环,接受系统产生的事件,并且进行分发,这些都是在exec中进行的。
下面举例说明:
1)首先看看下面一段示例代码:
- int main(int argc, char *argv[])
- {
- QApplication a(argc, argv);
- MouseEvent w;
- w.show();
- return a.exec();
- }
2)a.exec进入事件循环,调用的是QApplication::exec();
- int QApplication::exec()
- {
- return <span style="color:#ff6666;">QGuiApplication::exec();</span>
- }
3)QApplication::exec()调用的是QGuiApplication::exec();
- int QGuiApplication::exec()
- {
- #ifndef QT_NO_ACCESSIBILITY
- QAccessible::setRootObject(qApp);
- #endif
- return QCoreApplication::exec();
- }
4)QGuiApplication::exec()调用的是QCoreApplication::exec();
- int QCoreApplication::exec()
- {
- if (!QCoreApplicationPrivate::checkInstance("exec"))
- return -1;
- QThreadData *threadData = self->d_func()->threadData;
- if (threadData != QThreadData::current()) {
- qWarning("%s::exec: Must be called from the main thread", self->metaObject()->className());
- return -1;
- }
- if (!threadData->eventLoops.isEmpty()) {
- qWarning("QCoreApplication::exec: The event loop is already running");
- return -1;
- }
- threadData->quitNow = false;
- QEventLoop eventLoop;
- self->d_func()->in_exec = true;
- self->d_func()->aboutToQuitEmitted = false;
- int returnCode = eventLoop.exec();
- threadData->quitNow = false;
- if (self) {
- self->d_func()->in_exec = false;
- if (!self->d_func()->aboutToQuitEmitted)
- emit self->aboutToQuit(QPrivateSignal());
- self->d_func()->aboutToQuitEmitted = true;
- sendPostedEvents(0, QEvent::DeferredDelete);
- }
- return returnCode;
- }
5)QCoreApplication::exec()调用eventLoop.exec()进行事件循环;
- int QEventLoop::exec(ProcessEventsFlags flags)
- {
- Q_D(QEventLoop);
- //we need to protect from race condition with QThread::exit
- QMutexLocker locker(&static_cast<QThreadPrivate *>(QObjectPrivate::get(d->threadData->thread))->mutex);
- if (d->threadData->quitNow)
- return -1;
- if (d->inExec) {
- qWarning("QEventLoop::exec: instance %p has already called exec()", this);
- return -1;
- }
- struct LoopReference {
- QEventLoopPrivate *d;
- QMutexLocker &locker;
- bool exceptionCaught;
- LoopReference(QEventLoopPrivate *d, QMutexLocker &locker) : d(d), locker(locker), exceptionCaught(true)
- {
- d->inExec = true;
- d->exit = false;
- ++d->threadData->loopLevel;
- d->threadData->eventLoops.push(d->q_func());
- locker.unlock();
- }
- ~LoopReference()
- {
- if (exceptionCaught) {
- qWarning("Qt has caught an exception thrown from an event handler. Throwing\n"
- "exceptions from an event handler is not supported in Qt. You must\n"
- "reimplement QApplication::notify() and catch all exceptions there.\n");
- }
- locker.relock();
- QEventLoop *eventLoop = d->threadData->eventLoops.pop();
- Q_ASSERT_X(eventLoop == d->q_func(), "QEventLoop::exec()", "internal error");
- Q_UNUSED(eventLoop); // --release warning
- d->inExec = false;
- --d->threadData->loopLevel;
- }
- };
- LoopReference ref(d, locker);
- // remove posted quit events when entering a new event loop
- QCoreApplication *app = QCoreApplication::instance();
- if (app && app->thread() == thread())
- QCoreApplication::removePostedEvents(app, QEvent::Quit);
- while (!d->exit)
- processEvents(flags | WaitForMoreEvents | EventLoopExec);
- ref.exceptionCaught = false;
- return d->returnCode;
- }
6)eventLoop.exec()调用QCoreApplication的processEvents进行事件分发;
7)调用notify进行分发
QCoreApplication::sendEvent、QCoreApplication::postEvent和QCoreApplication::sendPostedEvents都调用notify进行事件分发;
- bool QCoreApplication::notify(QObject *receiver, QEvent *event)
- {
- Q_D(QCoreApplication);
- // no events are delivered after ~QCoreApplication() has started
- if (QCoreApplicationPrivate::is_app_closing)
- return true;
- if (receiver == 0) { // serious error
- qWarning("QCoreApplication::notify: Unexpected null receiver");
- return true;
- }
- #ifndef QT_NO_DEBUG
- d->checkReceiverThread(receiver);
- #endif
- return receiver->isWidgetType() ? false :<span style="color:#ff6666;"> d->notify_helper</span>(receiver, event);
- }
8)notify调用notify_helper进行事件分发;
- bool QCoreApplicationPrivate::notify_helper(QObject *receiver, QEvent * event)
- {
- // send to all application event filters
- if (sendThroughApplicationEventFilters(receiver, event))
- return true;
- // send to all receiver event filters
- if (sendThroughObjectEventFilters(receiver, event))
- return true;
- // deliver the event
- return receiver->event(event);
- }
9)从上面第8步的代码可以看出事件传递
传递的顺序是:首先传递给全局的事件过滤器,再传递给目标对象的事件过滤器,最终传递给目标对象。
http://blog.csdn.net/chenlong12580/article/details/25009095